Humans are subject to infection with a wide range of commensal and pathogenic organisms. Each pathogen requires an appropriate immune response to eliminate or control the invading organism and minimise pathology. Many pathogens have evolved strategies to subvert or manipulate the immune response and establish on-going infections. Similarly acute respiratory infection with virulent strains of influenza A virus are often poorly controlled by the immune system and can cause severe immunopathology and even fatality as a result of an inappropriate and excessive inflammatory response called a ‘cytokine storm’. Morbidity due to influenza infection and exacerbation by the immune response can vary greatly between individuals. The effect of underlying infection on the immune system could contribute to the variation in response. The aim of this project was therefore to determine if co-infection with two pathogens that establish on-going infections could alter the immune response to influenza A and impact the outcome of infection. Persistent infections with filarial helminths can cause debilitating disease and significantly impact the immune response toward a skewed TH2 or regulatory phenotype in order to control pathology. In contrast, infection with gammaherpesviruses in an immunocompetent host causes an initial inflammatory ‘anti-viral’ response before becoming an asymptomatic, latent infection. In an immunocompromised host, gammaherpesviruses can reactivate and lead to clinical presentation of disease. This suggests that these viruses require an on-going immune response to control all stages of infection. Both filarial helminths and gammaherpesviruses are common infections in human populations and therefore mouse models of these infections provide relevant systems to study their potential role in influenza virus infections. In a BALB/c murine co-infection model, latent infection with the rodent gammaherpesvirus MHV-68 led to significantly decreased weight loss and clinical signs following high dose infection with A/WSN/33, (a H1N1 influenza A virus). This was coupled with decreased immunopathology in the lung and fewer infiltrating lymphocytes in the alveolar spaces and around larger airways, although infectious virus titres were not significantly reduced. This response was coupled with a decreased production of inflammatory cytokines and chemokines in co-infected mice 6 days post infection which correlated with the amelioration of pathogenesis in these animals. A repeat of the study in 129Sv/Ev IFNγR knock out mice showed the same protective effect in the co-infected mice, suggesting IFNγ is not critical for the protective phenotype. Mice infected with latent MHV-68 alone showed a significant increase in expression of T cell chemokines in the lung and alveolar macrophages had a significantly increased production of suppressor of cytokine signalling (SOCS-1) suggesting latent MHV-68 infection may impact the phenotype of macrophages in the lung, modulating the response to influenza co-infection. A co-infection model with a persistent rodent filarial helminth, Litomosoides sigmodontis and A/WSN/33 was also established in BALB/c mice. The L4 developmental stage of L. sigmodontis infection had no impact on co-infection with A/WSN/33. Adult stage worms, however, appeared to have a protective effect against A/WSN/33 pathogenesis. Co-infected mice had significantly delayed weight loss and clinical signs 3-5 days post infection. CD4+ and CD8+ T cells in the lung draining lymph nodes had significantly reduced TH1 and TH2 phenotypes (measured by cytokine production) compared with singly infected controls. IFNγ secreting CD4+ T cells in the lungs of co-infected mice also secreted increased levels of IL-10, suggesting an increase in regulation of the inflammatory response to A/WSN/33. At the full patent stage of L. sigmodontis infection, co-infection with A/WSN/33 led to increased clinical signs and significantly exacerbated weight loss. CD4+ and CD8+ T cells in the lung draining lymph nodes were inflammatory in L. sigmodontis infected mice alone as well as co-infected mice and there were no differences in the percentage of CD4+ T cells in the lung secreting IL-10 and IFNγ between co-infected and influenza infected mice. A loss in regulatory responses during the patent stage of L. sigmodontis infection may therefore contribute to the loss of protection against A/WSN/33 at this time point within the co-infection model. Understanding the impact of an underlying infection on the immune system could provide immune mechanisms that could be exploited to increase vaccine efficacy against influenza and similarly help to provide better treatment for individuals infected with influenza A. These results may also help predict the outcome of influenza A infection in individuals already infected with highly immunogenic, on-going infections.

Malignant catarrhal fever (MCF), a disease that is usually fatal in cattle, is caused by two distinct but related bovine herpesviruses which are members of the genus Macavirus. The wildebeest-associated alcelaphine herpesvirus-1 (AlHV-1) occurs mainly in East and southern Africa, whereas the sheep-associated ovine herpesvirus-1 (OvHV-2) has an almost worldwide distribution. The natural hosts or carriers of these two viruses are subclinically infected. The 130 kilobase pair (kbp) AlHV-1 double stranded DNA genome consists of 18 open reading frames (ORFs) coding for structural proteins and approximately 50 ORFs coding for non-structural proteins. The 18 structural ORFs encode for 4 capsid proteins, 5 tegument proteins, 8 glycoproteins and a minor capsid scaffold protein. ORF8 encoding for glycoprotein B, is the most conserved of the proteins amongst gammaherpesviruses, whereas the minor capsid protein encoded by ORF65, is amongst the most variable. Thus, the minor capsid protein is one of the antigens of choice for the development of an ELISA for detection of AlHV-1 reactive antibodies and glycoprotein B could be of importance in developing a cross-protective vaccine for gammaherpesviruses. The naming and annotation of most of the AlHV-1 ORFs is based on comparison with related gammaherpesviruses and bioinformatics. Most of these ORFs are putative as there is no direct experimental evidence confirming that they code for any particular protein. In order to investigate whether the ORFs code for any proteins, two ORFs were targeted for in vitro heterologous expression. AlHV-1, isolate C500, was grown in fetal bovine turbinate (BT) cell culture and viral genomic DNA extracted. ORF8, the putative glycoprotein B, was amplified with a PCR assay and inserted into a mammalian expression vector, pCI. VERO cells were transfected with the recombinant vector. Expression of ORF8 was confirmed by an indirect immunofluorescence assay (IFA) with AlHV-1 polyclonal sera and rabbit anti-bovine IgG (whole molecule) FITC conjugate. Truncated forms of ORF8 were further expressed as baculovirus recombinants using the Bac-to-Bac baculovirus expression system. Expression of the truncated ORF8 was confirmed by SDS-PAGE and Western blot. AlHV-1 ORF65, the minor capsid protein gene, was amplified with a PCR assay from the viral genomic DNA and cloned in frame with a histidine tag in a bacterial expression vector, pCOLD I. Expression of the minor capsid protein was confirmed by SDS-PAGE and Western blot with the histidine tag monoclonal as well as AlHV-1 polyclonal sera. Orf65 was expressed in large quantities and column purified using the histidine tag. Orf65 was also expressed as a baculovirus recombinant using the Bac-to-Bac baculovirus expression system. Expression of the protein was confirmed by SDS-PAGE and Western blot with the histidine tag and AlHV-1 polyclonal sera. ORF65 expression in the baculovirus Bac-to-Bac expression system was up-scaled and the expressed protein column purified. Antibodies raised in chicken against the purified antigen were used successfully in an indirect immunoassay to detect AlHV-1 infected cells. An indirect enzyme-linked immunosorbent assay (ELISA) to detect antibodies against AlHV-1 was developed. It is based on the use of the AlHV-1 minor capsid protein as the capture antigen for antibodies. The primary antibodies are detected by the addition of enzymelabelled (horseradish peroxidase) protein G which detects bovid, ovid and wildebeest antibodies. Addition of a substrate of the enzyme, in this case, 3,3’,5,5’- tetramethylbenzidine (TMB), results in a colour reaction which is measured using spectrophotometric procedures. At a selected cut-off point of 18, the ELISA test has a sensitivity of 100% and a specificity of 100% and has been shown to detect AlHV-1 antibodies in cattle and wildebeest. The ELISA showed no cross-reactivity with sera raised in cattle against related viruses such as ovine herpesvirus 2, bovine herpesvirus 1, 2 and 4. The two expressed proteins used in this study were found to be amongst the antigens expressed in cattle suffering from malignant catarrhal fever. The experimental AlHV-1 indirect ELISA needs further validation and this research may be extended to determine the performance of these antigens as candidate subunit vaccines. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Veterinary Tropical Diseases / unrestricted